# What You'll Need:
→ Potatoes
01 - 3 pounds Yukon Gold or Russet potatoes, peeled and thinly sliced (about 1/8 inch)
→ Cheese Sauce
02 - 4 tablespoons unsalted butter
03 - 1 medium yellow onion, finely chopped
04 - 3 cloves garlic, minced
05 - 4 tablespoons all-purpose flour
06 - 2 1/2 cups whole milk, warmed
07 - 1 cup heavy cream
08 - 2 teaspoons Dijon mustard
09 - 1 teaspoon salt
10 - 1/2 teaspoon black pepper
11 - 1/2 teaspoon smoked paprika
12 - 2 cups sharp cheddar cheese, shredded
13 - 1 cup Gruyère cheese, shredded
→ Topping
14 - 1/2 cup shredded cheddar cheese
15 - 1/2 cup shredded Gruyère cheese
16 - 2 tablespoons chopped fresh chives (optional)
# Cooking Steps:
01 - Preheat the oven to 350°F. Grease a 9x13-inch baking dish with butter or nonstick spray.
02 - Arrange half of the sliced potatoes evenly in the prepared dish.
03 - In a large saucepan over medium heat, melt the butter. Add the chopped onion and sauté for 4 to 5 minutes until softened. Add the garlic and cook for 1 more minute.
04 - Sprinkle the flour into the saucepan, stirring constantly for 1 to 2 minutes to form a roux.
05 - Slowly whisk in the warm milk and heavy cream, stirring continuously until the mixture is smooth and begins to thicken, about 3 to 4 minutes.
06 - Stir in Dijon mustard, salt, black pepper, and smoked paprika.
07 - Remove from heat and whisk in the shredded cheddar and Gruyère cheeses until fully melted and smooth.
08 - Pour half of the cheese sauce over the first potato layer. Arrange remaining potatoes on top, then pour the remaining sauce evenly over them.
09 - Cover the dish with foil and bake for 45 minutes.
10 - Remove the foil, sprinkle the remaining cheddar and Gruyère cheeses on top, and bake uncovered for an additional 25 to 30 minutes until potatoes are tender and the top is golden and bubbly.
11 - Allow to rest for 15 minutes before serving. Garnish with fresh chives if desired.
